Basement Waterproofing (BS 8102:2022) Type A+A System vs Type A+C which did you go for?

[NailBiter]

On Page 5 titled 

More robust waterproofing solutions
https://www.riw.co.uk/uploads/whitepapers/RIW_BS8102_2022_WHITEPAPER.pdf

 

It states:

 

Quote

The guidance on combined protection has also been updated. The standard provides examples of which types of systems can be combined –

Type A+B, A+C, B+C, A+B+C - and now also includes a mention of Type A+A. However, also included in the guidance is the recommendation that where a combination is used, the systems should have different performance characteristics to ensure that both waterproofing systems are not compromised due to a common cause. For instance, a cement based coating and a modified epoxy coating, which have similar limitations when bridging dynamic cracks.

The 2022 update also recommends that the compatibility of the systems in practice should be considered to minimise the risks. A waterproofing specialist, such as RIW with extensive knowledge and experience, can provide guidance on the optimum configuration and combination of different systems and technologies to achieve the performance required.
 

Additionally, there is now an increased focus in BS 8102 on the protection and maintainability of waterproofing systems to ensure longevity. In fact, the servicing and maintenance section 10.3 has been revised to emphasise the importance of planning the maintenance, especially of type C (drained) systems.

We are using Nudura XR35 externally and Nudura one system internally and the walls are linked. For this reason I'm being told I need a Type A system (agreed) and a Type C system including treating internal walls. I can see the logic in this but I'd much rather have my waterproof perimeter on the exterior of the building even if it requires two systems.

It seems in the most recent version of the standard allows for a Type A + A system as long as the mechanical properties of the systems are different.

Is anyone taking this approach? We would of course still have drainage to the outside as per Nudura's documentation.

[Mike]

55 minutes ago, NailBiter said:

I'd much rather have my waterproof perimeter on the exterior of the building even if it requires two systems.

Personally I'd choose an external system, with a drained internal cavity as backup. That's mainly because, years ago, I knew someone who had an externally tanked system that leaked. It was a semi-underground extension to provide bedrooms for his kids. By the time the legal dispute was settled (solution: add an internal drained cavity) - the kids had left home.

[Conor]

We went with an external self adhesive bituminous membrane system on top of our ICF. We do have one corner of damp, reason for this tbc.

[NailBiter]

5 hours ago, Conor said:

We went with an external self adhesive bituminous membrane system on top of our ICF. We do have one corner of damp, reason for this tbc.

Which ICF system did you guys go for? Hopefully it's something simple for you guys like humidity vs seepage.

We would be going for a system like this and I guess if we were to go A+A possibly a spray on system before sticking it on?

I'm concerned by all the extra effort that will go into using a Type C system even though they are impressive in that other than silting up with lime (which can be present when throwing around a lot of concrete apparently) there aren't many catastrophic failure modes and most of the system can be tested (e.g. a floor flood test). It does present some requirements for maintenance too and rodding access is required at any change of direction. 

 

An internal moat doesn't sound appealing to me. 
 

It seems that the guidance allowing A+A systems was published in 2019 and hasn't disseminated fully yet. 

[scottishjohn]

we had tnaking problems with the old washhouse -- now a garge 

 the ground outside was right to top of the walls as can be seen if you lookat my thread 

original wall was 200years + old and very iffy

my builders solution 

build 4"block wall next to orighinal

stick on mebrane isidenew wall ,then gap and block wall  again gap filled with concrete

 time will tell if it was the right way

[George]

Type A + C for me. And over a long time period the Type A is essentially just slowing the amount of work the Type C needs to do.

 

Main thing is to stick to a single warranted system.

[Moonshine]

Type A + C for habitable areas for us, Type A into the garage area, I can put you onto some local guys who did ours. Pretty happy with them and their service.

[FM2015]

I think the main emphasis from BC is maintainable.  Types A and B tend to not be easily maintained/repaired.  Type C should be a fail-safe.  Most contractors we use essentially only guarantee type C.  

[NailBiter]

On 20/05/2024 at 12:07, Moonshine said:

Type A + C for habitable areas for us, Type A into the garage area, I can put you onto some local guys who did ours. Pretty happy with them and their service.

That would be great Moonshine thank you.

[Gus Potter]

On 18/05/2024 at 22:45, NailBiter said:

We are using Nudura XR35 externally and Nudura one system internally and the walls are linked. For this reason I'm being told I need a Type A system (agreed) and a Type C system including treating internal walls. I can see the logic in this but I'd much rather have my waterproof perimeter on the exterior of the building even if it requires two systems.

 

On 20/05/2024 at 11:52, George said:

Type A + C for me. And over a long time period the Type A is essentially just slowing the amount of work the Type C needs to do.

 

Main thing is to stick to a single warranted system.

Hiya Nailbiter.. good choice of name for this situation.

 

Good general advice from @George

 

For all.. a few of my thoughts.. in no particular order..

 

If you are a self builder and newish to the game (say have self built less than a couple of houses that have basements) then it can be a challenge to get your head around each part of the design.. say basement and superstructure. A key feature here is to recognise that the bit that goes on top (the top bit) can have a big influence on how the basement (call this the bottom bit) is designed and how much cost that will attract if you don't recognise that the top bit and bottom bit don't interact. There are big savings to be made here.

 

Self building tends to drive you down the road where you want to spend as little on say an SE / Architect etc as possible. You tend to split things up into different work packages.. it's the only way you can (with limited experience) to see conceptually how the finances will work. I've no problem with that, I've been a self builder in the past.. before I was an SE / Designer so can see both sides of the coin and I have myself isolated each work package... and thought.. I can steamline later I'll make a saving? I didn't but at least I still kept my shirt but I was younger then... too cocky!

 

On 18/05/2024 at 22:45, NailBiter said:

Is anyone taking this approach? We would of course still have drainage to the outside as per Nudura's documentation.

Every site is different. The design decisions you make are driven by many things.

 

Say you are planning a self build with a full basement, have one on my books at the moment.  My scope of works could be to act as an independant consultant who keeps a  brief on how we are developing the early design. The other part of my brief is to design the bits that no one wants to. These tend to be the nasty bits and relate to the common practice of say TF suppliers / basement designers shedding off design liability to the Client.

 

The main thing here is that we recognise that the actual concrete box basement could be braced by the floor at ground level.. here lies big savings! Also it there is a flotation risk ( as it's a full basement) and we are getting our heads round how we deal with that.

 

The actual basement design and tanking system is driven by for example the ground conditions, water table and how we are going to get rid of the foul and surface water... you don't want you sewage running back towards your basement which is an inviting sump!

 

We are spending time understanding this. The Client has spent targeted money on a site investigation.. they got me in early to comment on the scope of the SI so we have been able to discuss / plan together. Now we are getting close to being able to give the specialist basement designer a better quality of information which includes the Clients specific requirements which they have spent a lot of time putting on their wish list which needs to be met. All that saves money / time and hassle.

 

To summarise.. my Client and I  have not yet decided what type of water proofing we are going to adopt and in what combination. We know we will get something to work but can't do so until we have got lots of the drainage etc conceptually nutted out.

 

@NailBiter I think you need to get a handle on the ground conditions, drainage before you can take a view on what Nadura et al are saying? In fairness to them they can only give general advice.

 

If you want a bit of general advice post more info on your site. Do you have a full basement or a partial one for example where you can let any ground water out at the low end?